THE EFFECTS OF TIDAL CURRENTS ON THE RELEASE, ABUNDANCE, AND RECRUITMENT OF LARVAE OF SESSILE MARINE INVERTEBRATES

Previously we found that many sessile marine invertebrates recruited in slack water periods at low and high tide. It is unclear whether variations in larval release, local abundances of larvae, or larval responses to currents caused these patterns. To address this, we are using automated samplers to simultaneously sample larval release, abundance, and recruitment as functions of current regime. At each site the samplers are deployed with a current meter and computer controller that uses the current data to control sampling intervals. Sampling is divided into 4 periods: low and high water slack (<10cm/sec), flood and ebb (20-70 cm/sec). Concurrent seed shadow experiments also examine the effects of currents on the distance and direction that lecithotrophic larvae are transported before settling.

Initial results indicate that larval densities of lecithotrophic species are highest during ebb with recruitment highest at low-water slack, suggesting a local source of larvae. Larval densities of planktotrophic species were highest during flood with recruitment highest at high-water slack, indicating a regional source. Larval release seemed more closely tied to light than current.